Thought it appropriate to insert an article by Patricia Banner – the Flower Farmers Wife, featured in the publication Growing for Market back in 2010 to learn how to grow dahlias from cuttings. There is another copy of this article over at one of Banner Flower Farm blogs FieldofDahlias.com
As the flower farmers daughter, I think there is a particular aspect on this subject to learn how to grow dahlias from cuttings that probably needs addressing is a question from one of our customers,
Why do you say “Don’t save the tubers produced from the cuttings”?
Thus, there will be a part 2 to this article answering this question.
For now, here is the full article.
Take dahlia cuttings now for hoop-house planting
Dahlias are spectacular cut flowers that always command attention at the farmers markets. The main season for field-grown dahlias is late summer through fall, but if you have a high tunnel, you can get an early start by taking your own cuttings in January. Dahlia plants from cuttings, planted out in April in an unheated high tunnel, will produce harvestable stems by late May here in Michigan.
Taking dahlia cuttings is one of the easiest ways for a beginner to start the dahlia experience. It is also one of the most economical means of building one’s dahlia tuber stock. The cuttings are true descendants from the original dahlia plant. Many tubers will produce eight to 10 cuttings.
Most varieties of dahlias can be propagated without fear of violating plant patents. The exception is the ‘Karma’ dahlia series which are bred by the VerWeer brothers in the Netherlands. Bob Bosgraaf, Bosgraaf Greenhouses in Michigan, is the only grower in the United States licensed to propagate cuttings of the Karma dahlias.
To take cuttings, you can start with tubers you dug last fall, or you can purchase new tubers. To begin, place tubers in moist sand or potting soil at a temperature of 55-60°F. The top of the tuber should be about one inch below the soil line. We plant the tubers in gallon pots so that we can leave a plant to grow after we have finished taking cuttings.
Because the days are still short in January, and dahlias need long days for vegetative growth, we use supplemental lighting as soon as we plant the tubers. We extend the daylength to 14 hours, using 60-watt bulbs that are hung every four feet above the benches, about a foot above the pots. On sunny days, we turn on the lights for several hours in the morning and the evening, and on cloudy days we keep the lights on all day.
When the dahlia tubers send up shoots, usually within two weeks of planting, wait until the shoots have four leaves and are about 3 inches tall. Then cut the shoots off, about a dime’s thickness from the tuber. Remove the bottom set of leaves, leaving approximately 1/4 inch under the leaf node.
The tuber will send up more shoots; as these shoots appear, cut them off in the same way.
We root our cuttings in small, clear Solo condiment cups filled with dampened sand. We make two to three small slashes on the bottom of the cup with a knife so that the cuttings can take up water as needed. Punch a hole in the center of the Solo cup lid. Gently push the cutting carefully through the punched-out area on the lid. The lid is very important, as it holds the cuttings upright while they take root in the small containers.
Place the Solo cups in trays filled with water. Seedling flat trays without drainage holes work best; however, we have used cookie sheets, cake pans and Glad-type plastic containers that are approximately 2 to 3 inches high. Be sure to check on the cuttings often, and add water to the bottom of the trays only. The water level needs to come up halfway on the Solo cups. Place these containers carefully into a heat box.
We built our heat box from directions in a Growing for Market article several years ago. The box is made with two 2- by 8-inch boards nailed together with braces on the inside. The dimensions of the box are 8’ long x 3’3” wide x 16” tall. The bottom of the box is a piece of 3’ x 8’ corrugated tin. On top of the corrugated tin there is a 1-inch layer of foam insulation board with aluminum coating, aluminum side up. That is covered with a 2” layer of fine sand. Heating cable is then laid on the sand, spaced about 4.5 inches apart. We purchased 80 feet of Gro-Quick cables from Gloeckner Seed and a GC-1 thermostat. The cables cost $89, and the thermostat was $69. The thermostat is mounted to the side of the heat box. A piece of wire mesh over the sand holds everything in place. Another 4-8 inches of play sand is distributed over the entire top of the mesh and smoothed out evenly.
The heat box is kept at 65-70°F. Higher heat brings the cuttings along faster; however, they are not as strong. In the 65-70 degree range, the cuttings take about two weeks to root.
We use shade cloth over the heat box during the day if the sun is bright to prevent leaf burn. We have made a removable wooden cover with handles. At night, we place the wood cover over the box, which helps maintain an even temperature and reduce heat loss. During the warm days, the wood cover is easily removed.
You will be able to see the tiny roots forming on the dahlia cuttings since the plastic container is clear; most likely you will be examining the containers and plants often.
As soon as the cuttings are rooted, carefully cut away and remove the lid on the Solo cup, taking extreme caution so as Dahlia to not disturb any root growth. It may be necessary to gently tap the bottom of the Solo cup to release the root ball.
At this time, we plant the cuttings in 3 1/2- to 4-inch square pots filled with a good quality potting soil. Many peat-based soils dry out too quickly and unevenly. The best combination is one third compost, one third potting soil and one third garden soil. Here in Western Michigan, we have a company by the name of Renewed Earth that will mix a potting mixture formula to any requirements a grower may have.
The plants should be grown under 14 hours of daylight until they are about 8 inches tall. Again, it’s important to use supplemental lighting to keep the plants in vegetative growth; without it, the plants will shut down and start producing tubers.
When growing the cuttings in 4-inch pots, monitor the root growth. Root-bound plants produce stunted dahlia plants. It may be necessary to bump the plants up to gallon pots. We do not pinch the dahlia plants, except for two varieties, ‘Rebecca Lynn’ and ‘Jessie G’. With those, we remove the terminal stem just above the second pair of leaves when the plant is about 12 inches in height. Young plants recover quickly from pinching, and a fuller plant then develops.
Planting in the Hoop-house
In a 20 x 96-foot hoop-house, we have two 3-foot wide outer beds along the sidewalls and one 4-foot-wide bed down the center. The outer beds have three rows of plants spaced 12 inches apart, or 276 plants per bed. The center bed has four lines of plants, 368 plants per bed.
Before planting the dahlias, we lay Hortanova support netting on the beds to provide a planting grid. Once the plants are in the ground, we remove the netting and lay drip tape on the beds, one line per row of plants to ensure that each plant receives enough water. In the past, we replaced the support net but we always found it difficult to weed and even harvest with it. So this year we are going to support the plants with a stake-and-weave system. We fertilize through the drip lines with a high-phosphorus fertilizer, 9-45-15. The nitrogen level needs to be low; otherwise, there will be lush, green growth with fewer blooms.
A positive to growing dahlias in a high tunnel is the plants shoot up faster, and aren’t nearly as bushy as field-grown dahlias. Because it is early in the season and the night temperatures are cooler, the colors are more vibrant. We also have observed that dahlias grown in a high tunnel produce more blooms and re-bloom more quickly. Growing under cover offers rain and wind protection as well as fewer pests.
The negative side for us is that by August it is too hot in the high tunnels, and the dahlias start to fade. By this time, however, the field grown dahlias begin producing heavily.
DO NOT SAVE TUBERS PRODUCED FROM CUTTINGS.